Centerpost Engineering
The centerpost of the spherical tokamak carries the highest field, current, and neutron load in the machine, making it the hardest component.
The core of a spherical tokamak
In a spherical tokamak the central column, the centerpost, is where the toroidal-field conductors pass through the middle of the machine. Because the geometry is compact, this column is slender and carries the most concentrated loads in the entire device: high field, high current, mechanical stress, and neutron flux together.
What the centerpost must withstand
- Magnetic field approaching the 16.84 T peak, with associated Lorentz stress
- High current density in the toroidal-field conductors
- Neutron loading, since it sits close to the plasma
- Thermal loads from resistive and nuclear heating
Why it is the pacing engineering problem
Every advantage of the compact spherical design, high beta, small size, high field, converges as stress in the centerpost. If the centerpost cannot be built to carry these loads reliably, the whole configuration fails. This is why the magnet gate G2 and centerpost design are central to risk retirement.
Design and materials
The centerpost design draws on REBCO high-field magnet practice and structural analysis to carry Lorentz and thermal loads within material limits, with neutron shielding to protect the conductors over the machine's life. Its centerpost lifetime under neutron fluence is one of the flagged engineering questions the program tracks.
The centerpost is a design for a machine not yet built. It is the component the first-of-a-kind unit most needs to validate on hardware.